1. Field of the Invention
The present invention relates to a circuit assemblage and a method for functional checking of a power transistor, which are usable for power currents in vehicles.
2. Description of Related Art
Large currents in vehicles, especially those of motors or positioning devices, solenoid valves, and thermal loads, are increasingly being switched using MOSFETs and IGBTs. Both have, because of their insulated gate, a relatively high input resistance on the order of, for example 1012 ohm. When a voltage is applied from outside between the gate and source (in a MOSFET) or between the gate and emitter (in an IGBT), and the connection to the voltage source is then broken, the gate potential is retained for a relatively long time, e.g. several seconds, because of the high input resistance.
If an interruption occurs at the contact point because of aging or vibration, for example due to a break in the solder join or a detachment of the bond to the gate, the gate potential of the transistor can no longer be influenced from outside. If the transistor was previously in a conductive state, it will persist in that state and continue to allow power currents to pass. In the case of loads controlled solely by way of their power current terminals (such loads being common in vehicles), a shutoff is thus often no longer possible.